From London's Tower Bridge to a 110-story Chicago skyscraper, it would seem that the most brazenly effective way to boost visitor numbers at the world's most vertiginous urban landmarks is to install a glass-bottomed floor, walkway or, gulp, exterior slide.

Now, as part of an ambitious $100 million preservation and renovation project, the Space Needle joins the ranks of other iconic observation towers (the Eiffel Tower, Toronto's CN Tower, the Auckland Sky Tower, the Tokyo Skytree, et al.) to give intrepid visitors the option of shuffling, stretching, sitting and taking 800 selfies atop glass panel flooring. And in a never-seen-before twist, the Space Needle's new glass floor, located a heart-quickening 500 feet above Seattle, revolves.

Who said an aging World's Fair leftover can't learn new tricks?

Completed in 1962 as the Space Age-y centerpiece of the sprawling Seattle Center entertainment and cultural campus, the Space Needle has undergone numerous tweaks, upgrades and alterations over the decades: zippier elevators, an overhauled rotating restaurant, the addition of a controversial sky beam and, in 2008, the lanky historic landmark's first-ever professional power-washing.

Throughout it all, the emphasis has remained on the stunning panoramic views of Seattle and environs afforded from up top. Mountains! Lakes! Bays! Islands! Construction cranes!

With the newly unveiled glass-bottomed "experience" named the Loupe now open, visitors can look out and straight down.

Profile skyline photo of Space Needle Mid-century majesty: While its exterior may appear unchanged, the observation levels of the 56-year-old Space Needle have been radically revamped to improve views. (Photo: Chad Copeland/Space Needle LLC)

A true glass act

Headed by Olson Kundig, the lauded Seattle-based design practice known for oh-so-Pacific Northwest commissions that meld seamlessly into their rugged natural surroundings, the Space Needle's newly unveiled "spacelift" focuses on expanding views at the top of the 605-foot-tall tower with massive amounts of glass — 196 percent more of it than before, to be exact, with 10 different varieties and a total of 167 tons used.

"Walls, barriers — even floors — have been removed and replaced with structural glass revealing a visceral experience the visionary designers of the Space Needle could only dream of," reads a recent press release.

The Loupe, the renovation's see-through star attraction, consists of 10 layers of tightly bonded glass that together weigh 37 tons. This considerable thickness may provide reassurance to some more anxious guests although it doesn't do anything to dispel the crippling fear that comes along with peering straight down into the Seattle Center from 50-stories up. (It's curious — but also unsurprising — that absolutely no one in the below promotional video appears to be even the least bit apprehensive. There's not even the slightest glimmer of trepidation in these wide-smiling faces.)

As for the revolving part, the floor is powered by a dozen 9.1-kilowatt motors and 48 rollers that enable it to make a full clockwise rotation every 45 minutes. It can be sped up, slowed down or programmed to rotate in a counter-clockwise direction. At full speed, the floor makes a full rotation in just under 20 minutes.

"The original revolving floor in the restaurant went clockwise for one rotation in 47 minutes," Karen Olson, chief marketing officer for the Space Needle, explains to USA Today. "So we're going to start this with one clockwise rotation every 45 minutes and see if we need to adjust it from there."

(SkyCity, the Space Needle's rotating fine dining restaurant better known to Seattle old-timers as the Eye of the Needle, is temporarily closed. The world's oldest still-operating rotating restaurant, SkyCity is scheduled to reopen later this year.)

Looking down from the Loupe Do look down: Composed of 10 layers of super-strength glass, the Loupe offers a distinct and (mildly) terrifying new view from the Space Needle's lower observation deck. (Photo: John Lok/Space Needle LLC)

Floating staircases and transparent seating

In addition to the Loupe there are other notable new features found at the tippity-top of the Space Needle in the flying saucer-esque observation complex.

A grand cantilevered staircase dubbed the Oculus Stairs now connects the two main observation levels. At the bottom of the gravity-defying stairs on the 500-foot-level is a glass-floored oculus that "reveals the Space Needle's superstructure as well as the elevators and counterweights ascending and descending." (The Ring Level, a service-oriented mezzanine with refurbished restrooms, is also accessible via the staircase.)

'Skyriser' benches on the Space Needle's outer observation deckAscending the staircase to the 520-foot level, visitors will find a spruced-up indoor observation deck outfitted with floor-to-ceiling glass windows. Newly widened doors lead to the adjacent open-air outer observation platform, now encased with 48 seamless, outward-sloping glass panels in lieu of the old partial walls and wire security caging.

Here, visitors can hunker down and snuggle up in one of 24 inclined glass benches dubbed "Skyrisers." Per a press release, the innovative benches provide guests with an "intense feeling of floating above the city" if they feel so inclined.

Thanks to a new custom-designed ADA lift, the outer observation deck is now also fully accessible to all.

Back on the 500-foot level near the Loupe, a new wine bar offers timid guests liquid courage by the, ahem, glassful.

Mugging for photos on the Loupe, a 'new experience' at the Space Needle Acrophobia-free and loving it: These visitors to the Loupe, billed as the world's first-ever revolving glass floor, don't seem in the least freaked out by their surroundings. (Photo: John Lok/Space Needle LLC)

Bigger, better views (as originally intended)

If the Space Needle's glass-heavy makeover — also known as the "Century Project" — seems wildly complex from a construction and engineering standpoint, that's because it was. For starters, specific challenges come into play when renovating a structure that's perched 500 feet in the air atop a slender, hourglass-shaped tripod pedestal. And as the folks at the Space Needle point out, the tower is also an "active" structure that expands, sways and twists depending on wind and temperature.

But as Alan Maskin, a partner at Olson Kundig, explains to Architectural Record, the the massive undertaking has been more about stripping things away as a means of closer aligning the Space Needle to the way it was supposed to be.

"Our work has really been about subtraction," Alan Maskin, a partner at Olson Kundig, tells Architectural Record. "Peeling away all these walls, tiny little doors and floors and, in almost every case, replacing them with glass." He adds: "This was our chance to show off the original engineers' and architects' work."

As Architectural Record explains, because the Space Needle is a locally designated historic landmark but not listed on the National Register of Historic Places, Olson Kundig and numerous project partners waded through significantly less bureaucratic red tape during the cutting-edge renovation process.

The project team at Olson Kundig worked closely with the Seattle Landmarks Preservation Board, architecture historians, the tower's original surviving designers and others over a span over several years in conceiving the "spacelift." This way, the renovation would be "consistent with the original design intent and respect the character-defining features of the Space Needle."

What's more, the firm enjoyed "unusual freedom from constraints that so often tether renovations of historic structures" due to the fact that the Space Needle is privately owned by the family of the same construction firm that erected the tower in just 400 days for the 1962 Seattle World's Fair (aka the Century 21 Exposition.)

Construction photo of the Loupe Loupe-in-the-making: While plans for the first phase of the Space Needle's $100 million 'spacelift' took years to finalize, construction wrapped up in just under a year. (Photo: Rod Mar/Space Needle LLC)

At its opening, the flamboyantly futuristic Space Needle was the tallest man-made structure west of the Mississippi — today, it's the sixth tallest building in Seattle and the fourth tallest observation tower in the United States. It would seem that the Wright Family, which forked over $100 million to renovate a structure that cost $4.5 million to originally build, enthusiastically embraced Olson Kundig's view-expanding overhaul.

"We needed to update some of the aging mechanical and electrical systems in this 56-year-old building originally designed to look like a flying saucer on a stick," Space Needle CMO Olson tells USA Today. "And we figured, while we're up there, let's update the experience and expand the view."

View from Space Needle observation deck Simply breathtaking: Thanks to ingenious engineering work and 175 tons of glass, the 360-degree Puget Sound views from atop the Space Needle are now better than ever. (Photo: Rod Mar/Space Needle LLC)

With the first and largest phase of the renovation now complete (the observation decks amazingly remained open during much of the construction), crews will continue work on other upgrades including optimizing the tower's energy usage so that it can achieve LEED Silver certification, painting the exterior and once again updating the elevator system. Pre-work included a seismic upgrade of the structure's steel legs so that it can better withstand significant tremors.

No word if the Wheedle, the Space Needle's furry mythological resident mascot, will receive upgraded digs.

A ticket to ride one of the Space Needle's elevators to the dramatically glass-ified observation levels will set you back $27.50 and $37.50 depending on the time of day. Since 1962, over 60 million visitors have made the trip up to the top.

Inset Skyriser photo: Space Needle LLC

Matt Hickman ( @mattyhick ) writes about design, architecture and the intersection between the natural world and the built environment.

Space Needle renovation includes knee-buckling new attraction
A massive makeover at the 1962 Seattle landmark yields an unnerving world's first: a revolving glass floor.